1. Field of the Invention
The present invention relates to a pressure adjustment structure for a presser foot of a sewing machine, and more particularly to a sewing machine provided with a pressure adjustment structure for adjusting an elastic pressure of a presser bar. Two supporting frames are connected with a horizontal arm to strengthen the whole structure of the sewing machine.
2. Description of the Prior Art
A conventional pressure adjustment structure for a presser foot of a sewing machine is such a structure that a presser bar connected with a presser foot is provided with an elastic structure, and the elastic structure is such that a cam-shaped adjustment element is pushing against a connecting bar. The structure of the connecting bar is complex, as shown in FIG. 5, wherein a top of the presser foot 90 is provided with a presser bar 91, an elastic member 92 is mounted on the presser bar 91, a top of the elastic member 92 is pressed by a gasket 93, and the gasket 93 is pressed and driven by one end of the connecting bar 94 which is made by a folded plate-shaped member. The middle part of the connecting bar 94 is pivotally connected to a pivot shaft 95, and the pivot shaft 95 is pivotally connected to one end of a horizontal arm of the sewing machine. The other end of the connecting bar 94 is pushed against by a cam portion of an adjustment element 96 which is pivotally disposed on one end of the horizontal arm. By rotation of the adjustment element 96, the connecting bar 94 rotate an angle around the pivot shaft 95, and the end of the connecting bar 94 pressed against the gasket 93 and one end of the elastic member 92 is caused to move downward to compress the elastic member 92, thus producing a prestress. However, such a structure still has following disadvantages:
1. The arrangement of the connecting bar 94 and the pivot shaft 95 is highly complex, and its stability is limited, because the connecting bar 94 is made by a folded plate-shaped member, the folding process carried on the connecting bar 94 is difficult, and the connecting bar 94 must cooperate the pivot shaft 95 to be positioned, so the assembling of the present invention is inconvenient, and the stability of the connecting bar 94 and the pivot shaft 95 is limited.
2. The indirect pressure is difficult to control: the connecting bar 94 rotates around the pivot shaft 95 to press the gasket 93, it is difficult to control the pressure, and the pressure is not stable due to a deficiency of the rotation of the connecting bar 94.
3. The strength of the whole structure is low: the adjustment element 96 is pivotally connected with a plate-shaped supporting frame at one end of the horizontal arm only by nuts being inserted through holes located around the supporting frame, and the connecting force is limited. Pressures are always produced in different directions during adjusting the adjustment element 96, thus causing a distortion of the supporting frame and a limited strength of the structure. The position of the adjustment element 96 is also affected, so that a pressure of the elastic member 92 will not be adjusted exactly.
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages.